The invention concerns the heating of electrically conductor flat products, this heating being obtained by scrolling through electromagnitude induction. A known device employed for this contains the following essential components:
A transfer system keeping the flat product to be heated in a heating plane and scrolling it along a longitudinal transfer direction in this plane. The width of the product is laid in a transverse direction also in this plane and its thickness in a direction of flow, each of these directions being perpendicular to others. The transverse position of the product to be heated can be adjusted.
Inductor excitation windings.
Electricity supply sources to supply these windings with an electric current periodically variable according to the time and with controlable amplitude, so that they thus produce a magnetic flow varying like this current.
And magnetic inductor circuit to channel this flow and form a heating flow through the product to be heated more or less along the said direction of flow.
The invention applies to the frequent case where heating must be homogeneous over the whole surface of the product.
Amongst the devices known to obtain this heating, most of them use a magnetic field whose profile is uniform over the greater part of the width of the product. This profile is corrected on the edges to obtain homogeneous heating over the whole width by organizing the distribution of the closing currents. The homogeneity along the lengths results from the longitudinal scrolling of the product.
This is notably the case in the British Pat. No. 1546367. The corrections to the edges are obtained by various devices (coils, or additional magnetic bridges, air-gap modifications, . . . ) which complicate the construction and must be adapted to the induced reaction of the product, this reaction depending on the latter's characteristics: thickness, resistivity.
Another known device said to be "sqaure mesh" does away with the above difficulties. It is described in the document No. FR-A 2538665 (the French Pat. No. EN 82 21906 of Dec. 28, 1982). The inductor consisting of windings and magnetic circuits obtains square meshing of the heating flow with a sinusoidal distribution of the magnetic field along the two directions parallel to the sides of the squares. If the product has a width containing an integer number of times the pitch of the meshing, heating is then homogeneous without any correction to the edges. However if the width of the product does not contain an integer number of times the pitch of the meshing, a heterogeneous temperature develops on the two edges. To reduce this heterogeneity it is possible firstly to modify the excitation current of the meshing elements opposite these edges, secondly to provide a relatively small meshing pitch so that the heat difused by conduction provides acceptable homogenization in this area. However a small pitch of the meshing may be a handicap given that the inductible surface capacity varies in the same way as the fourth power of this pitch, without so much ensuring a sufficient homogenization through conduction in the product if the scrolling speed is relatively high (short transfer time). Additional inductors can thus be added opposite the edges, but this introduces the constructional complexity indicated above.